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Filtergrams obtained in Ca II H, Ca II K and H-alpha are often employed asdiagnostics of the solar chromosphere. However, the vastly disparate appearancebetween the typical filtergrams in these different lines calls into questionthe nature of what is actually being observed.  We investigate the lack of obvious structures of magnetic origin such asfibrils and mottles in on-disk Ca II H and K images by directly comparing atemporal sequence of classical Ca II K filtergrams with a co-spatial andco-temporal sequence of spectrally resolved Ca II 854.2 images obtained withthe Interferometric Bidimensional Spectrometer (IBIS), considering the effectof both the spectral and spatial smearing. We find that the lack of finemagnetic structuring in Ca II K filtergrams, even with the narrowest availablefilters, is due to observational effects. Signatures of fibrils remain howeverin the temporal evolution of the filtergrams, in particular with the evidenceof magnetic shadows around the network elements. The Ca II K filtergrams do notappear, however, to properly reflect the high-frequency behavior of thechromosphere. Using the same analysis, we find no significant chromosphericsignature in the Hinode/SOT Ca II H quiet-Sun filtergrams.  The picture provided by H-alpha and Ca II 854.2, which show significantportions of the chromosphere dominated by magnetic structuring, appears toreflect the true and essential nature of the solar chromosphere. Data which donot resolve, spatially or spectrally, this aspect may misrepresent the behaviorthe chromosphere.

The solar chromosphere at high resolution with IBIS: III. Comparison of Ca II K and Ca II 854.2 nm imaging